A conveying system for pasty material such as sludge or comminuted food waste or the like typically has an eccentric screw pump having a stator, a rotor that rotates in the stator, a suction housing forming an intake port at a low-pressure side of the stator, and preferably a pressure housing with output port that is connected to the a high-pressure side of the stator.
Such an eccentric screw pump is from the group of rotary displacement pumps that are used to convey a wide variety of media and in particular highly viscous liquids in a wide variety of industrial sectors, with the media or liquids to be conveyed often having high solids contents. In the context of the present invention, the eccentric screw pump is used to convey pasty material and thus highly viscous liquids with (high) solids contents.
The stator is made of elastic or elastomeric material, for example, and is usually surrounded by a one-piece or multipart stator casing or stator housing. The eccentric screw pump has a drive for the rotor and preferably a coupling rod in the suction housing that is preferably connected via a drive-side joint to a drive-side shaft and via a rotor-side joint to the rotor, with the coupling rod allowing eccentric rotation of the rotor. An eccentric screw pump is preferably constructed as a hopper pump in which a feed hopper is connected to the intake port. In such an embodiment for conveying pasty or highly viscous media with solids content, the coupling rod is preferably equipped with conveying tools, for example with an auger or with conveyor paddles promoting transport of the material from the intake port to the rotor.
In practice, there is a need to transport pasty material or media such as dewatered sludge, for example, over long distances, and this poses great challenges to local wastewater treatment, for example, since a substantial pressure drop in the conduit caused by the high viscosity and abrasiveness of this material/medium must be overcome. These pressure losses scale proportionally over the length of the conveying route, which makes conveyance over distances in the range of kilometers extremely difficult. The commonly used pump solutions must build up high pressure in order to overcome the pressure losses, so that they are limited by their pressure rating to a maximum conveying distance. In addition, high back pressure places an extreme load on the pumps, resulting in frequent, time-consuming, and expensive maintenance cycles due to wearing of the rotor-stator structures and/or the joints. When eccentric screw pumps are used for such long conveying routes, commensurately large, heavy-duty eccentric screw pumps must be used with considerable maintenance and associated costs.
Alternatively, sequential conveyance solutions with multiple drives such as conveyor belts or augers are used in practice. Disadvantages include high energy consumption and maintenance costs, and an open design is often associated with corresponding odor nuisance or rewatering dried sludge by rain. Such conveyance solutions are also inefficient for vertical or angled transport. The use of closed piping usually requires the use of multistage eccentric screw pumps or, alternatively, piston pumps, that are suitable for high-viscosity media and high pressures; however, due to the high back pressure, they require a relatively high drive power and are thus associated with high energy consumption and high maintenance.
Pneumatic conveyance and so-called plug conveyance in particular are also known from practice, but these are mainly used to transport loose bulk materials. Such a method and device for the pneumatic conveyance of bulk material is known for example from WO 2001/002274. The bulk material is to be conveyed from a low to a high level, with the bulk material being first conveyed substantially horizontally, then pneumatically raised and subsequently conveyed pneumatically. The initial conveyance occurs in the form of discrete plugs of bulk material, and the bulk material is lifted in the form of a largely continuous flow of bulk material.
A conveyor system with a pipeline for the transport of short, similar fluent plugs of a granular or powdery material is also known for example from DE 33 19 076. This system consists of a conduit and branch lines parallel thereto. In addition, a feeder, for example a pumps, is provided that has a seal against a pipeline pressure caused by a fluid pressure source. In principle, the feeder can also be an eccentric screw pump with rotor and stator. In any case, the pump is downstream from a material-holding chamber at the upstream end of which a connection for the fluid pressure source is provided so that fluid pressure can be applied continuously to the conduit via the holding chamber on the intake side. In addition, at least one opening for allowing entry of a small quantity of the fluid into the conduit is provided in the subsequent conduit for material plug transport. When using an eccentric screw pump, it is also proposed to that a cellular wheel sluice be provided at the downstream-end holding chamber whose intended purpose is not only to better seal the pump against the prevailing pressure in the conduit, but also to reduce the size of the material emerging from the pump.
In addition, devices for conveying moist and mushy material in pipelines in terms of a plug transport are known from DE 874 877 and DE 559 237.
Finally, DE 42 03 571 describes a mobile device for producing lightweight concrete with a screw mixer and a screw pump to which a pressurized chamber of a compressed air mixing and conveying machine is connected via a connecting line.